Quetiapine (Seroquel ®), an atypical antipsychotic registered for use in schizophrenia, which has a very low propensity of extrapyramidal and endocrine side-effects, has also been studied as an adjunct in OCD. In an open trial, ten patients with OCD who had not responded to at least three previous treatments with a SRI at maximum dose and duration were assigned to receive quetiapine in addition to a SRI for 8 weeks. Given the efficacy of quetiapine in treatment resistant patients, and given its rapid onset of action (4-6 weeks), it is postulated that the combination of a low dose atypical antipsychotic and a standard dosage of an SRI as a treatment for patients with OCD might increase the number of responders as well as the effect size.